At present, Wireless Local Area Network (WLAN) develops rapidly in the field of wireless network, and a demand is for WLAN coverage is growing. An industrial standards group of Institute of Electrical and Electronic Engineers (IEEE802.11) defines a series of most common WLAN technique standards such as 802.11a, 802.11b and 802.11g successively; then, other task groups appear successively and are committed to developing improved standards involved in the present 802.11 technique, for example, the 802.11n task group raises a request of High Throughput (HT), which supports a data rate of 600 Mbps; the 802.11ac task group further proposes a concept of Very High Throughput (VHT), which increases the data rate to 1 Gbps. Thus, new protocol needs to be backward compatible with the previous protocol.
In the 802.11 standard, one Access Point (AP) and multiple Non-AP Stations (STAs) associated with the AP form a Basic Service Set (BSS). The WLAN defined by the IEEE802.11 enables multiple stations to share a wireless channel by utilizing a mechanism of Carries Sense Multiple Access with Collision Avoidance (CSMA/CA).
In the IEEE 802.11 technique, one channelized set refers to a set consisting of multiple big-bandwidth channels (such as 40 MHz, 80 MHz, 120 MHz, 160 MHz channels) which consist of multiple 20 MHz channels defined from a predefined or fixed starting frequency point within a given frequency band. The 20 MHz channel forming the set also is called a basic channel; other channels consisting of these basic channels also are called big-bandwidth channels. A big-bandwidth channel contains a basic channel which is called a primary channel, wherein the primary channel is configured to broadcast control information. In a channelized set, each basic channel has a unique channel number.
In the technique defined by the IEEE802.11 series standards, an authorization-free Industrial Scientific Medical (ISM) frequency band is channelized into multiple 20 MHz channels according to the bandwidth of the 20 MHz basic channel. The interval between the central frequency points of every two adjacent channels is 5 MHz; and the channel is numbered according to the specified or predefined starting frequency point. The IEEE802.11 uses multiple channels defined above as working channels. For example, on a 2.4 GHz frequency band, the IEEE802.11 defines 14 adjacent 20 MHz channels as available channels, wherein each available channel is overlapped with its adjacent available channel with an interval of 5 MHz between the central frequency points; another example, on a 5 GHz frequency band, the IEEE802.11 defines five 20 MHz channels between 5.735 GHz and 5.835 GHz as available channels, wherein each available channel is not overlapped with its adjacent available channel with an interval of 20 MHz between the central frequency points. The available channel refers to a group of non-overlapped basic channels defined in a channelized set or a set consisting of these basic channels; the working channel refers to an available channel currently used or to be used by a wireless apparatus.
In some conditions, the frequency planning in some countries can not be fully utilized based on the above definition of channelization. For example, on the 5 GHz frequency band in China, the frequency band applicable to the WLAN totally is 125 MHz of frequency band between 5.725 GHz and 5.850 GHz, and there exists a high-efficiency channelization scheme capable of dividing the frequency band into six 20 MHz available channels at present. However, there is a problem of central frequency point offset between this high-efficiency channelization scheme and the existing 5 GHz channelization scheme, so that the WLAN apparatus can not perform simple extension in the high-efficiency channelization scheme like in the existing channelization scheme; particularly when one same WLAN apparatus supports the existing channelization scheme and the high-efficiency channelization scheme simultaneously, the WLAN apparatus can not perform channel scanning according to the existing mechanism and thus can not establish a WLAN network.
Therefore, how to plan the process implemented by an apparatus, which supports the existing channelization scheme and the high-efficiency channelization scheme simultaneously, to perform channel scanning and establish a network is an urgent problem to be solved in the new generation of 802.11 protocol based on big-bandwidth.